In some refrigerant systems, the refrigeration load requirements vary. For example, in some grocery store environments, one refrigerant system controls the air conditioning requirements, as well as the cooling load requirements for refrigerated food displays. These load requirements vary depending on the time of day, the ambient air temperature both inside and outside the store, the types of foods stacked in the refrigerated food displays, and the number of customers ingressing and egressing the store. The variations in load are most prevalent during the hottest, most humid days in the summer.
To compensate for these load variations, many refrigerant systems incorporate a compressor of variable capacity to accommodate the changing load demands. In some refrigerant systems, one large, single speed compressor, having enough capacity to account for peak load demands is cycled on and off during periods of low load requirements such as at night. However, this prior art technique is inefficient because it is difficult to maintain a constant, controlled temperature using only one cycled compressor and repeated on-off cycling of the compressor can damage the compressor. Other refrigeration systems include racks of smaller, constant speed compressors operating in parallel. Most of the compressors operate continually. During periods of peak load requirements, other reserve compressors are operated to account for the increased load demands. Even though the use of more than one compressor offers some advantage by having a more increased control over the refrigeration compressor capacity, the use of multiple compressors is expensive, and the installation and maintenance costs for the system are increased.
In another system, a variable speed electric motor drives the compressor. The motor includes an electronic inverter for varying the speed of the motor over a wide range. Refrigerant pressure or temperature is sensed and the motor speed adjusted to vary the speed and thus, capacity of the compressor. This system does offer some additional control over load variations as compared to other prior art systems. However, the complexity of the control electronics associated with the system and the use of an invertor for the electric motor can increase maintenance costs. Additionally, the complex electronics associated with this type of system typically only can be serviced by specially trained technicians. Many refrigeration technicians primarily are trained only in the mechanical workings associated with a refrigeration system. Thus, some refrigeration technicians may not be able to repair a breakdown in the electronics of the system.
As a result, it has been determined that a mechanical control for varying the speed of a refrigeration compressor for accommodating load variations is more desirable. It also has been determined that a preferred mechanical control includes variable pitch pulleys retained on a constant speed motor shaft and a compressor shaft and drivingly interconnected thereto by a belt. By effecting adjustment of the pulley pitch on both the motor and compressor, the relative speed of the compressor can be adjusted. Thus, complex electronics to control the speed of the motor are not needed. Additionally, the use of two variable pitch pulleys establishes a fixed center distance between the motor and compressor shafts and maintains a constant belt tension at maximum and minimum speed ranges so that the belt life is extended as compared to the belt life used in a system where the center distance between the motor and compressor shaft is varied.
Some older prior art refrigeration apparatus have incorporated belt interconnected variable pitch pulleys on a motor and compressor shaft, such as disclosed in U.S. Pat. Nos. 2,130,995 and 2,320,432 to Henney. In both patents, a pneumatic diaphragm is directly actuated by a temperature sensor. The pneumatic diaphragm pushes a mechanical lever mechanism directly connected to a movable pulley to change the pitch of same. This type of mechanical mechanism is inefficient for several reasons. As compared with more recent electrically powered motive means, only a small force can be generated to move the pulleys, making use of that mechanical type of device on larger motors impractical. Also, the diaphragm and lever mechanisms apparently do not provide means limiting axial movement of the pulley components so as to avoid driving the compressor at too low a speed and causing low oil flow with the resultant compressor burn-up. Additionally, the patents do not disclose that the motor and compressor can be fixedly mounted to a preferred rack having upper and lower levels to mount the motor and compressor to minimize floor space usage. The complex mechanical mechanisms incorporating the temperature controlled pneumatic diaphragm and lever mechanism could make installation of a motor and compressor on a preferred rack difficult.
Other prior art patents disclose similar pneumatically controlled mechanisms as well as fluid coupling such as commonly used in automobiles. These also suffer similar and other drawbacks.
It is therefor an object of this invention to provide a refrigerant system having a controlled variable speed drive for a compressor and which includes variable pitch pulleys mounted on a constant speed motor and compressor shafts, a belt interconnecting the pulleys and electrically powered motive means for varying the axial position of one motor pulley component for changing the speed of the compressor.
It is another object of this invention to provide a refrigerant system having a controlled variable speed drive for a compressor and which includes variable pitch pulleys mounted on constant speed motor and compressor shafts, a belt interconnecting the pulleys, electrically powered motive means for varying the axial position of one pulley component, and means operatively connected to said electrically powered motive means for deactivating the same for limiting axial movement of the movable motor pulley component away from the other motor pulley component to thereby avoid driving the compressor at too low a speed.
It is still another object of this invention to provide a refrigerant system having an upright rack for mounting on upper and lower levels thereon, a constant speed motor and refrigerant compressor and a controlled variable speed drive for the compressor which includes variable pitch pulleys mounted on a constant speed motor and compressor shafts, a belt interconnecting the pulleys, and electrically powered motive means for varying the axial position of one motor pulley component and change the speed of the compressor.
It is still another object of this invention to provide a controlled variable speed drive apparatus for an electric motor having variable pitch pulleys thereon and coupled by a belt to variable pitch pulleys mounted on a power input shaft of a refrigerant system compressor and the like and which includes pivotally mounted lever means extending transversely of the axis of the motor pulley and electrically powered motive means operatively connected to one end of the lever for imparting pivotal movement to the lever and changing the pitch diameter of the motor pulley to change the speed of rotation of the power input shaft.